1. Field of the Invention
The present invention is related to an electrodeless sulfur lamp, and particularly to an electrodeless sulfur lamp, which do not use magnetron.
2. Description of the Background Art
There are various sources of lighting: an incandescent lamp using heat radiation, a fluorescent lamp of which an electric discharge tube uses a fluorescent material, a high intensity discharge (HID) lamp using electric discharge within a high-pressurized gas or steam, and a plasma lighting system (PLS) lamp using electrodeless discharge.
The various lamps have their respective advantages and disadvantages. The incandescent lamp is excellent in color rendition and small-sized, but inefficient in emitting light and short-lived. A switching-on-light circuit of the incandescent lamp is simple and low-priced. The fluorescent lamp is efficient in emitting light and long-lived, but larger in size, compared to the incandescent lamp. The fluorescent lamp requires the subsidiary switching-on-light circuit. The HID lamp is light-efficient and long-lived, but requires much time between switching off light and switching on light. In addition, the HID lamp, like the fluorescent lamp, requires the subsidiary light-switching circuit. The PLS lamp is much long-lived and efficient in emitting light, compared to the others, but high-priced, and low in power consumption. In addition, the PLS lamp requires the subsidiary switching-on-light circuit.
The PLS lamp is the latest one. An electrodeless sulfur lamp, which belongs to the PLS lamp, is a highly-efficient full-spectrum electrodeless lighting system whose light is generated by sulfur plasma that has been excited by microwave radiation. The electrodeless sufur lamp consists of a golf ball-sized quartz bulb containing several milligrams of sulfur power and argon gas at the end of a thin glass spindle. The bulb is enclosed in a microwave-resonant wire-mesh cage. A magnetron bombards the bulb with 2.45 GHz microwaves. The microwave energy excites the gas to five atmospheres pressure, which in turn heats the sulfur to an extreme degree forming a brightly glowing plasma capable of illuminating a large area. At an initial stage of switching on light, the electric discharge occurs in argon, which is a buffer gas. As temperature increases, the electric discharge occurs in sulfurous steam, thereby emitting white light which is excellent in color rendition.
The first prototype of the electrodeless sulfur lamps were 5.9 kW units, with a system efficacy of 80 lumens per watt. The first production models were 1.4 kW with an output of 135,000 lumens. Later models were able to eliminate the cooling fan and improve efficiency to more than 100 lumens/watt.
A problem with the conventional electrodeless sulfur lamp is that the life of magnetron is life-shorted, compared to the quartz bulb. The design life of the quartz bulb is currently approximately 60,000 hours. However, the design life of the magnetrons is currently only about 15,000 to 20,000 hours. This requires frequent replacement of the life-expired magnetrons with new ones before the life of the quartz bulb expires. The development in the magnetron generating the micro-wave is relatively slow, which contributes to lowering an energy transfer rate.